The N54 head is not BMW's best work. Why? It did not need to be to hit their goals. People forget this is not an M motor and BMW did not create a high revver or top end monster with the N54. The good part of that is you can pick up nice gains on the N54 head in the aftermarket.

VTT goes into some of these details in their technical article regarding the N54 head. Read it below.

There are a bunch of things needed, among them:
Coolant passages are different
Head bolts are 1 mm smaller
On the exhaust side it's the same bolt pattern but larger ID on the ports and OD for the gaskets which means you're going to need custom exhaust manifolds or do other trickery.

It's a high flowing head -flows way better than the N54, obviously- but you have to be willing to do custom work, or pay someone else to do it for you to just be able to bolt 'er on. For some it may be worth it, but for most I think just doing a nice PNP on a N54, maybe even add a cam and you'll see plenty of real world gains with zero fitment issues.

We were asked by a couple guys "what about a stock N53 head, how does that flow?" We have no idea, and in our opinion that's not a great option for cost savings as you still have to do all the other things to make 'er fit on an N54... if you're gonna do it, while you're in there may as well PNP too!

Is it worth even thinking about a PNP N54 head on a stock N54 block with stock internals? For street only, perhaps?

Only if you can't hit your desired hp #s with your turbo(s) and fuel. I mean you can make more HP than the stock block can take with an off the shelf turbo kit. From that perspective, no need to work the head etc.

I personally do not see why you would want to build a head and add cams on a stock block unless you were running small turbo(s) for spool reasons or because of a class restriction.

The bang for your buck is not there on stock turbos unless you wanted to take the stock turbo world record. Which would be comical. I am surprised VTT has not done that yet, even if just for $#@!s and giggles. Weld the wastegates shut and #sendit

A fully built head is like what 3k+? add another 1k for cams. 4k uninstalled is pricey unless you are chasing records.

It's a really nice upgrade. I'd love to do it but I won't be able to justify the cost.
I already have GC turbos and I often run them at 21 psi on the street. Sometimes up to 25 psi.
I have run 27 psi a couple of times but at the time that was about the limits of my fuel supply.

They can probably do 30 psi but I feel like that's in a bit of a danger territory with the car. Detonation, cracked cylinder liners. Head lift. Plus on a stock drivetrain I worry that parts there will not last long.